The present invention generally pertains to alignment of satellite antennas and is particularly directed to a system for causing an antenna controller for a satellite antenna to determine the alignment position of the antenna for a given satellite.
The alignment position of a satellite antenna is controlled by an antenna controller, and must be determined for each of a plurality of satellites stationed in geosynchronous orbit above the Earth's equator in sight of the antenna. Typically, the antenna is attached to an antenna mount by an actuator and is rotated about a polar axis on the antenna mount moving the actuator in order to achieve alignment with a given satellite. Alignment data is displayed by a television monitor that is coupled to the antenna by a satellite receiver. The controller is operated to move the actuator to rotate the antenna into alignment with a given satellite. Alignment is determined by observing the quality of the television signal being received from the satellite and displayed by the monitor. The alignment position is indicated by a position count that is displayed by the monitor. Upon determining that the antenna is aligned with the given satellite, the alignment position count is stored in a memory location within the controller that is associated with the given satellite so that the antenna can be rotated to a position in alignment with the given satellite simply by accessing the stored alignment position count associated with the given satellite and causing the controller to move the actuator to rotate the antenna until the antenna position corresponds to the accessed count.
Once the antenna is aligned with a given satellite, the respective skews of the linear polarization axis of the antenna for matching the linear polarization axis of odd-numbered and even-numbered channels received from the given satellite must be determined. The odd-numbered and even-numbered channels received from any given satellite are skewed ninety degrees with respect to each other in order to reduce interference between adjacent channels.
For a given channel (which may be either odd-numbered or even-numbered), the skew of the antenna for matching the linear polarization axis of such channel as received from the given satellite is determined by causing the controller to rotate a probe within a mechanical polarizer of the antenna and observing the quality of the television signal being received from the given satellite and displayed by the monitor. Upon determining the skew at which the linear polarization axis of the antenna is matched with the linear polarization axis of the received channel, the skew data for such channel is stored in a memory location within the controller that is associated with such channel for the given satellite so that the antenna can be skewed to match the linear polarization axis for such channel of the given satellite whenever the antenna is rotated to a position in alignment with the given satellite simply by accessing the stored skew data associated with such channel of the given satellite and causing the controller to rotate the probe until the probe position corresponds to the accessed skew data. Since the angular relationship between the odd and even numbered channels for the given satellite is known, the installer uses the measured skew data that has been determined for one channel to calculate the skew data for the other channels, and the calculated skew data is stored for each of the channels of the given satellite.
Once the alignment position and the respective skews are determined for a given satellite, data indicating the determined alignment position and the respective determined skews for the given satellite are stored in the antenna controller.
Presently, there are over thirty satellites within sight of North America. Consequently, a substantial portion of the time spent in installing each new satellite antenna is spent in separately determining and storing the alignment position and skew data for each of these many satellites.